<div>
  <mat-form-field floatPlaceholder="auto">
    <input matInput [(ngModel)]="vmA.a" type="text" required placeholder="A">
  </mat-form-field>
</div>

<div>
  <mat-form-field floatPlaceholder="auto">
    <input matInput [(ngModel)]="vmA.b" type="text" required placeholder="B">
  </mat-form-field>
</div>

<div>
  <button mat-button (click)="onSubmit()">确定</button>
</div>
<div>
  <button mat-button (click)="onReset()">重置</button>
</div>

<div>
  {{mA | json}}
</div>
<div>
  {{vmA | json}}
</div>
<div>
  {{vmA.isDirty}}
</div>
